235 tuning problem

I am trying to sort out a 236 I6 that is down on power with a zenith carb. When trying to drive up a considerable hill the motor slows down - while showing a 'lean' condition of low 16's to mid-upper 15's afr - when down gearing to 3rd the engine goes to over-rich in the 12's and can easily pull the hill.
It is a 235 motor with the 'rotating' distr, i have rebuilt the distr and it has new vacuum pot and the vacuum lines to the carb are steel and leak free. I haven't had a vacuum gage on it while doing the hill test.
I have advanced the timing as much as i can, i can't really say what it is as they are kind of hard to read.
When driving on typical highways the afr is in the 14s'.
If you replace the zenith with a rochester you can pull the same hill without loss of power.
The two carbs have the same throttle bore - 1 11/16ths, i haven't verified the venturii.
Any ideas why the zenith would be so much weaker?
Thanks, oj

 

I think you have answered your own question, put the Rochester back on and forget about the Zenith. Those Rochesters were/are good carbs on inline Chevys.

 

Yep, run what the engine likes and be done with it. Evidently it likes the Rochester a lot better than he Zenith. It may be that there is a blocked or partially blocked circuit in the Zenith or that one or more settings are off on it as far as running it on the 235 go but if the Rochester works why change?